Thought I would reach out to the solar tech-heads today. I wrote previously that I thought I had a problem with one of my 3 LifePo4 batteries (1x230ah + 2x205ah). Turns out that it wasn’t actually a problem, I was still getting my full amp hours from the “bank” of batteries; one would just unload faster than the others. However, I already had put into motion replacing all my batteries…which would increase the overall power storage by 20%.

Current power storage capability 32.8kWh…about 40 hours of power with no additional sunlight.

After the upgrade the power storage capability 41kWh…about 49 hours of power with no additional sunlight.

I thought I would share the whole thought process on how I was going to configure the new battery bank. Why is that important? There is a balance between cost and benefit when it comes to installing solar components. But the overriding factor is safety…1) don’t injure anyone handling the components and 2) don’t burn down the house from a fire that starts from the solar equipment/install.

There are two additional factors involved here –

1. There are some efficiencies to be gained by having each battery “brain” (mini-computer) hooked to each others; and the “master brain” (mini-computer) of my overall solar system. Having the batteries talk to each other coordinating their charging/discharging, etc. does help. And the system’s “master brain” can better coordinate the interaction of all system components.
2. Below is a picture of the current battery side of the system. As you can see it looks a bit conflicted and confused. Although it works fine the aesthetics leave something to be desired. If the time comes to sell our place, heaven forbid, having a neat professional installation will, if not add value, will surely not detract from it. And yes, I will do a before and after picture to show what I mean.

To get the most out of this post you need to have a basic understanding of electricity and solar. But if you don’t, that is okay, you can always ask me questions.

First off is the electricity I currently use:

• Average AC load: 8.5aAC – 20aAC (1kw – 2.4kw), Daily Average 20kWh
• Normal Max AC load: 37aAC – 85aDC (2kw – 434kw)
• Maximum AC Amperage: 84aAC (42aAC per each AC leg – each inverter)
• Maximum DC Amperage: 194aDC (97aDC each leg – each inverter) – (2.3 DC amps for each 1 amp AC)

Proposed Battery Bank Design –

Each Battery Bank –

• Battery bank consists of 2 battery sets
• Each battery set consists of 2 batteries each
  • Batteries parallel daisy chained with 6” x #2awg (200a capacity rated at that length)
  • Set connected to Lynx with 24” x #2awg (200a capacity rated at that length)
  • Each set capable of 100a (based on internal BMS & circuit breaker)
• Each battery bank is connected to system via The Lynx Class T unit (1000a busbar)
• Each of two battery banks’ capable of 200a (split between 2 battery sets)
• Each of two battery banks’ over current protection device is 225a Class T fuse housed in the Lynx Class T unit

Issues / Resolutions –

1. Issue – Protecting 2awg wire between batteries.

Resolution – Battery internal BMS (100a) & internal circuit breaker (125a) protects the 2awg wire between batteries. 2awg rating for 6” length is 200a capacity.

2. Issue – Protecting 2awg wire connecting battery set to Victron Lynx Class T unit.

Resolution – Battery BMS (100a) & circuit breaker (125a) protects 2awg wire between battery set and Lynx. 2awg rating for 24” length is 200a capacity.

3. Issue – Protecting each bank from the other bank due to dead short.

Resolution – Lynx Class T unit has 225a Class T fuse on each bank.

4. Protecting system due to dead short in batteries.

Resolution – Lynx Class T unit has 225a Class T fuse on each bank.

New Battery Bank DC Loads –

• System
  • High Average: 20a
  • Normal Max: 85a
  • Maximum: 194a
• Each of two battery banks
  • Average: 10a
  • Normal Max: 42.5a
  • Maximum: 97a
• Each set of two batteries each
  • Average: 5a
  • Normal Max: 21a
  • Maximum: 49a
• Each battery
  • Average: 2.5a
  • Normal Max: 10.5a
  • Maximum: 24.5a

Battery Nominal/Maximum for Charge/Discharge (as per battery spec sheet): 75a nominal 100a maximum

The Victron Lynx Class T unit w/2 battery bank connections

• Each bank has dedicated 225a (20kAIC) fuse for over-current protection

Worst Case OPerational Scenario –

Problem: 3 out of 4 battery sets go off line. Dumping maximum 194a draw onto one battery set.

Outcome: Maximum draw still withing rating of 2awg wire between each battery, from battery sets to Lynx. And, current spread out over 2 batteries in set is still under 100a of BMS cutout if the draw is split equally between each battery in the set. And still under 125a of each battery’s circuit breaker if the draw is split equally between each battery in the set. If full draw hits a single battery before damage can be done to #2awg wire the BMS will shut down the battery and the battery internal circuit breaker will open stopping the flow of current.

If the current would somehow manage to keep flowing and increasing in amperage, the 225a Class T fuse will blow at the upper end of the #2awg wire carrying capacity before the wire fails.

Summary –

Solar power is complex but not un-doable for the average person. The key is learning and then applying commonsense to any problem once that problem is understood. Here I had no complicated problem…just had to apply the basic of electricity to the problem and the solution would be clear. Although, when “opinion” is added in, then there could be a number of correct answers.

Remember the overriding factors; 1) safety – don’t get anyone hurt, 2) safety – don’t burn the house down. Both are accomplished by the new battery bank configuration. Also, accomplished is economy. I was able to use a whole bunch of existing equipment and supplies such as wire/cable.  And also accomplished were the side benefits of some increase in efficiencies, some increase in stored power, and better overall system quality.

Part #2 will be which battery brand I chose and why.

Personal Note: I thought you might get a kick out of seeing my current battery bank. And yes, I will show an “after” picture as well.

Articles in this Series –

SOLAR: New Battery Bank – Part #2

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Related Articles –

• Trouble in Solar Paradise
• Update (2/24/2025) (no trouble in solar paradise after all)

 

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Q & A Time…Ask me a solar question or send me a message…

 

 

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